Most commercial unsaturated acids (i.e. oleic acid) are derived from animal tallow (by-product of the meat industry), tall oil (by-product of paper mills) or natural vegetable oils.
Fat splitting processes are well known in the art. The most common methods are:
1) Twichell process;
2) Batch autoclave process;
3) Continuous process; and
4) Enzymatic process.
In Twichell process, the fat is hydrolyzed at a temperature of 100° C. to 105° C. and at atmospheric pressure for 12 to 48 hours. Alkyl-aryl acid or cycloaliphatic sulfonic acid with sulfuric acid (0.75–1.25% w/w) are used as catalysts. Yields of 85%–95% are obtained. The main inconvenients resulting from this process are the catalyst handling, long reaction time, tendency to form dark-colored acid and high labor cost.
In the batch autoclave operations, the fat is hydrolyzed in the presence or absence of a catalyst. Live steam is injected continuously at the bottom while venting a small amount thereof to maintain the desired agitation and operating pressure. After settling and formation of an aqueous and a fatty acid phase, the fatty acid phase is treated with mineral acid. The fatty acid phase is further washed with water to remove traces of the mineral acid. Under catalytic conditions (i.e. zinc, calcium or magnesium oxides) the fatty acid phase is reacted for a period of 5 to 10 hours at 150° C.–175° C. A high yield of about 85%–95% is obtained. Without catalyst the fatty acids phase is reacted for a period of 2 to 4 hours at a high temperature (240° C.) to give similar yields. The main inconvenients resulting from this process are the catalyst handling and high labor cost.
In continuous operations also known as the Colgate-Emery process, a single-stage countercurrent high pressure splitting is carried out for fat hydrolysis. The fat is introduced by means of a sparge ring from the bottom of the splitting tower while water is introduced by the top. The crude fat passes as a coherent phase from the bottom to the top, while heavier splitting water travels downward as a dispersed phase through the mixture of fat and fatty acids. The high temperatures involved (250° C.–260° C.) associated to high pressures (725 psi) assures degrees of splitting up to 98% in only 2 to 3 hours. The principal inconvenients of this process are the high cost associated with the equipment and the restriction to relative clean starting materials.
In enzymatic operations, the lipase from Candida rugosa, Aspergillus niger, and Rhizopus arrhizus had been studied at temperatures of 26° C. to 46° C. for periods of 48 to 72 hours. Even though 98% of splitting is claimed there is no commercial process available until now. The principal inconvenient of this process is that because enzymes work very well over a specific substrate under specific conditions. Therefor, when the starting material is composed of more than one product, the reaction is less selective. Long reaction times and great volumes required to satisfy the optimal concentration are also current problems involved in this kind of procedure.
Fractionation of free fatty acids is commonly performed by distillation of tall oil. Tall oil is recovered in most paper mills by acidulation of the soap skimming from black liquor. Crude tall oil (CTO) consists of a mixture of fatty acids (40%–45%), resin acid (40%–45%) and various neutral components (i.e. hydrocarbons, wax alcohols, sterols, esters and residues). About 40% to 50% of the fatty acids contained in tall oil are oleic acid, while another 35% to 45% are linoleic acid. Higher quality of tall oil fatty acids, TOFA, (less than 2% of resins acid) can be obtained by distillation through two columns: a rosin column and a fatty acids column.
Oleic acid is probably the most important unsaturated fatty acids (UFA) because many applications have been developed for its use in different fields (i.e. cosmetics, chemicals, lubricants, textiles, etc.). Separation of oleic acid form tall oil distillates requires additional refining steps. Best known-process for fractionation of fatty acids by crystallization from solvent is the “Emersol” process, developed by Emery Industries Inc. in 1934. Different American patents used different solvents (methanol: U.S. Pat. No. 2,421,157; acetone: U.S. Pat. No. 2,450,235 and methyl formate: U.S. Pat. No. 3,755,389) to separate saturated fatty acids from unsaturated fatty acids. The process was optimized by addition of crystallizing promoters (neutral fats, tallow, and glycerol tri-stearate). One more refined promoter is described in Australian patent AU-28434/92. It is the reaction product of: 1) a polyhydric alcohol (i.e. glycerol, pentaerythritol, trimethylol pentane, etc.), 2) a dicarboxylic acid (i.e. adipic, oxalic, succinic, azelaic, glutaric and tartaric) and 3) a fatty acid.
All these processes require explosion proof installations and low temperature refrigeration systems.
Other methods for producing oleic acid involve separation over molecular sieves (U.S. Pat. Nos. 4,529,551 and 4,529,551); lithium soap separation (U.S. Pat. No. 4,097,507), urea complexation (U.S. Pat. Nos. 2,838,480 and 4,601,856) and complexation with dienophiles (U.S. Pat. No. 5,194,640). All these process have the inconvenient of a high cost operation associated to the use of chemicals required.
Dry fractionation technology was originally developed for treatment of animal fat (i.e. beef tallow) in the 60's. Since this time, many improvements were performed in response to the ever-increasing demand of the industry for new products with very specific requirements. Two main sources are now the target of this technology: 1) vegetable oils such as palm oil, soybean oil, sunflower oil, rapeseed oil, groundnuts oil, cottonseed oil and palm kernel oil and 2) animal fats such as beef tallow, milk fat, lard and fish oil.
These fats and oils are mainly composed of triglycerides, diglycerides and monoglycerides (i.e. a broad range of melting points) constituting a large number of intersoluble glycerides that are very difficult to separate by dry fractionation (i.e. solvent free crystallization). The separation of a liquid fraction (i.e. olein, used in food oil) and a solid fraction (i.e. stearin, used in shortening and margarine) can be achieved through dry fractionation.
In the present invention, dry fractionation was used to separate purified free fatty acid obtained by splitting the residual oils and greases recuperated from industrial and commercial operations (i.e. trap greases, yellow greases and brown greases).
The free fatty acids obtained from these starting materials are mainly constituted by unsaturated fatty acids, such as mainly oleic acid, linoleic acid, linolenic acid and saturated fatty acids such as palmitic acid and stearic acid. The range of melting points for these limited numbers of products, in comparison with all the possible combinations presented by glycerides, was shown to be wide enough to perform a highly selective separation.
Vegetable oils (i.e. triglycerides) were the first fuels used in diesel engines. They were subsequently abandoned because of major problems associated with their use (i.e. injector fouling, ring sticking and varnish build-up on the cylinder walls). As it is known, these problems are the result of high viscosity and high reactivity of polyunsaturated fatty acids present in triglycerides.
More efficient and economical petroleum-based fuels rapidly shifted these vegetable oils fuels. Today fuels are composed of mixtures of hydrocarbons derived from mineral oils. However, it is well known that exhaust gases from internal combustion of mineral fuels (CO, NOx, SOx, etc.) are shown to be very polluting. Moreover, in view of the limited mineral oil reserves and their increasing cost, there is a demand for renewable fuels that could replace petrol hydrocarbons or would permit the existing resources to be more effectively used.
Since the introduction of vegetable oil fuels (i.e. biodiesel) in the forties, much work has proceeded to increase its viability as a fuel substitute. In recent years, there has been a considerable amount of research worldwide on alternative diesel fuels. Biodiesel research programs, based on vegetable oils, are centered in eliminating the former problems (high viscosity and reactivity), the quality of emission, waste minimization and cost.
Viscosity problems were overcome by a drastic reduction of the molecular weight of branched triglycerides into linear monoesters more similar to straight hydrocarbons in regular diesel. The procedure of conversion involves a transesterification reaction with an alcohol. This reaction is preferably carried out in excess of alcohol (i.e. methanol or ethanol) and in the presence of a catalyst (i.e. sodium or potassium hydroxide). The products from the reaction are:
a) esters of vegetable oil;
b) glycerin;
c) alcohol (non-reacted excess) and
d) residual and spent catalyst.
At the end of the reaction, products are separated in two phases: an upper non-polar ester rich phase and a lower polar glycerin phase. The non-reacted alcohol and the residual and spent catalyst are distributed between the ester and glycerin phases. Moreover, some low molecular weight esters are dissolved in the glycerin phase. As each one contaminates both phases, many attempts to improve phase's separation have been developed.
Low glycerin content in biofuels is required to avoid clogs of the injection nozzles during combustion. Austria has been the first country to set a national biodiesel standard with maximum glycerin content (0.24% total and 0.02% free). Actually these values are recognized in many countries including the American National Biodiesel Board (NBB).
In the case of biodiesel fuel obtained from soy oil, 20% of crude glycerol is produced as a by-product and that represents a major effluent problem. The market for very high purity glycerol is limited and it requires very expensive purification. To overcome effluent problems, development projects were focused on different uses of the glycerol phase.
U.S. Pat. No. 5,145,563 (Culbreth et al., 1992) describes the use of ethers of glycerol as extractive distillation agent.
U.S. Pat. No. 5,308,365 (Kesling et al., 1994) describes the use of glycerol ethers mixed with biodiesel fuels to improve emissions content.
U.S. Pat. No. 5,476,971 (Gupta, 1995) describes reacting pure glycerol with isobutylene in the presence of an acid catalyst in a two phases reaction to produce mono-, di- and tri-tertiary butyl ethers of glycerol.
U.S. Pat. No. 5,413,634 (Shawl et al., 1995) describes use of ethers of glycerol as an additive to enhance physical properties of cement.
U.S. Pat. No. 5,424,467 (Bam et al., 1997) described the use of glycerol as a solvent for washing the ester phase to carry out the excess of methanol and the catalyst.
U.S. Pat. No. 6,015,440 (Noureddini, 2000) describes the elimination of the glycerin phase by converting it to ether derivatives by reacting glycerol with isobutylene in order to obtain only one phase (alcohol esters & glycerol ethers).
All these attempts to improve glycerol elimination and/or valorization require additional costly steps. It is quite evident that even in view of known prior art, the presence of glycerol as a by-product of the transesterification of triglycerides present in oils continues to be a problem.
Many of the problems related to the presence of glycerol could be overcome by utilizing other starting material other than vegetable oils (i.e. triglycerides).
Free fatty acids (FFA) obtained by fractionation of residual oils and greases recovered from industrial and commercial operations (i.e. grease trap waste: GTW) could be successfully used in the production of the aforementioned biodiesel. However such products may exert a strong odor during its processing.